Well who better to resolve this quandary than me?
When I came on as the writer, it was in version 2, so the "step" was already in place. That said, I picked up the story with the idea that "step" is the way it was. I also thought that what Retro said was pretty true. The step relation makes it easier to move quickly into sexual action without it feeling fake, so I prefer to write "incest" stories that way.
So, if you like it better if they are blood related, the patch is for you. If you don't mind the step- in there, or even prefer it, than I hope you enjoy what I'm writing